This invention relates to a plating bath for electrodeposition of aluminum, having a long bath life, also having a good operability in handling, and yet having a high current efficiency and conductivity, and a plating process making use of the bath.
Plating for electrodeposition of aluminum can be carried out with difficulty using a plating bath of an aqueous solution type, because of a large affinity of aluminum for oxygen and a lower potential thereof than hydrogen. For this reason, the plating for electrodeposition of aluminum has been hitherto carried out using a plating bath of a non-aqueous solution type, in particular, a plating bath of an organic solvent type.
This plating bath of an organic solvent type typically includes baths comprising AlCl.sub.3 and LiAlH.sub.4 or LiH dissolved in ether, and those comprising AlCl.sub.3 and LiAlH.sub.4 dissolved in tetrahydrofuran (see, for example, D.E. Couch et al. Electrochem., Vol. 99, (6), p.234).
All of these plating baths, however, contain very active LiAlH.sub.4 or LiH in the bath, and hence it may react with oxygen or water which may exist therein, to decompose, resulting in a lowering of current efficiency and also a shortened bath life. They also have the problem that they use organic solvents having so a low boiling point that they are highly in danger of explosion or burning. As other plating baths of an organic solvent type, a plating bath has been proposed, comprising triethylaluminum and NaF dissolved in toluene (R. Suchentrunk, X. Werkstofftech., Vol. 12, p.190). In this instance also, however, there is a problem in handling the triethylaluminum, which is highly dangerous, and it is considered difficult to put the bath into practical use in an industrial scale.
As discussed in the above, the conventional techniques have succeeded for the time being in settling the technical subject that the plating for electrodeposition of aluminum is carried out, but, because of employment of chemical substances which are difficult to handle, they all have disadvantages in the bath life and operability, leaving problems in widely and commonly using them as techniques for practical use.